Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.

Chirality reveals symmetry breaking of the fundamental interaction of elementary particles. In condensed matter, for example, the chirality of electrons governs many unconventional transport phenomena such as the quantum Hall effect. Here we show that phonons can exhibit intrinsic chirality in monolayer tungsten diselenide. The broken inversion symmetry of the lattice lifts the degeneracy of clockwise and counterclockwise phonon modes at the corners of the Brillouin zone. We identified the phonons by the intervalley transfer of holes through hole-phonon interactions during the indirect infrared absorption, and we confirmed their chirality by the infrared circular dichroism arising from pseudoangular momentum conservation. The chiral phonons are important for electron-phonon coupling in solids, phonon-driven topological states, and energy-efficient information processing.

The results of our nationwide, population-based study suggest that patients who undergo anaesthesia and surgery may be at increased risk of dementia.

Two-dimensional transition metal dichalcogenides (TMDCs) have shown great promise in electronics and optoelectronics due to their unique electrical and optical properties. Heterostructured TMDC layers such as the laterally stitched TMDCs offer the advantages of better electronic contact and easier band offset tuning. Here, we demonstrate a photoresist-free focused ion beam (FIB) method to pattern as-grown TMDC monolayers by chemical vapor deposition, where the exposed edges from FIB etching serve as the seeds for growing a second TMDC material to form desired lateral heterostructures with arbitrary layouts. The proposed lithographic and growth processes offer better controllability for fabrication of the TMDC heterostrucuture, which enables the construction of devices based on heterostructural monolayers.

New variant Creutzfeldt-Jakob disease (vCJD) was first identified in the UK in 1996, and was causally linked to bovine spongiform encephalopathy. Herein we report the first case of vCJD in Taiwan: a 34-yearold man who had lived in the UK between 1989 and 1997. The patient presented with depression, irritability, personality change, painful feet and allodynia, followed by gait ataxia and cognitive impairment. Electroencephalograms did not show the typical appearance of sporadic CJD. The cerebrospinal fluid 14-3-3 protein immunoassay was negative. Brain magnetic resonance imaging revealed high signal lesions involving bilateral caudate nuclei, left lentiform nucleus, bilateral dorsomedial thalami and pulvinar on fluid-attenuation inversion recovery, T2-and diffusion-weighted imaging. Prion protein gene analysis showed homozygous for methionine at codon 129. The patient developed akinetic mutism at 16 months and died at 28 months after onset. The clinical presentation and neuroimaging findings were compatible with the vCJD cases reported since 1996, and met the World Health Organization Case Definition for probable vCJD. In this communication, we also review two other cases of vCJD in Asia. All three cases were assumed as imported cases from the UK because of the residential or travel history of the patients.